Encapsulation of an active material is generally known and many polymers have been referenced and used. A typical configuration for coating large granules is sometimes referred to as core-shell encapsulation. In core-shell encapsulation, water soluble actives are encapsulated in an insoluble (or very slowly soluble) plastic.
Poly(vinylidene dichloride) (PVDC) latex emulsions also known by the trademarked names Daran in emulsion form and Saran in solid film form, has been widely used in this regard and is a highly chlorinated plastic, which has environmental concerns. It would be beneficial if a more sustainable polymer can be used that meets the required performance criteria.
In addition, coating with PVDC can be overly time consuming and costly. The cleaning of process equipment is difficult due to its low solubility in all aqueous cleaning solutions and standard cleaning solvents, with the exception of tetrahydrofuran (THF). The polymer cures overly fast in typical coating equipment, requiring that a very low coating temperature be used to avoid premature latex curing and spray nozzle blockage. Therefore, a replacement polymer latex which facilitates faster coating speed is also desirable.
Other polymers suggested for such use include a range of different polyurethanes. These polymers are synthesized using isocyanates and therefore also have environmental concerns in their manufacture and use. Bisphenol A (BPA) epoxy resins have also been suggested for use as barrier coatings for use in a water containing environment, however such materials are under scrutiny for their content of BPA.
US 2013/255951 discloses a single latex polymer with a single Tg value for use in a delayed release coating. WO 2013/090341 discloses coating and paint compositions of a single latex polymer, and the compositions show improved block resistance, scrub resistance, and tack resistance.
There exists a need to provide granules of a water-active material with a barrier coating that has good film formation in the process of encapsulating the active, that has good performance as a barrier under the required temperature and/or pressure in the aqueous environment, and that has good performance from an environmental and/or health safety standpoint with minimized extractable materials.